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Indoor mould: a growing health problem

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Household mould, a type of filamentousfungi, is a problem that most of us have had to deal with at some time oranother

Household mould, a type of filamentous fungi, is a problem that most of us have had to deal with at some time or another. It thrives in damp, humid spaces such as base-ments, bathrooms, air conditioners, windowsills and wall cavities and, once it takes hold, can cause serious damage to your home.

However, indoor mould can cause serious damage to your health, too. There's growing evidence that living in a damp and mouldy environment can lead to all manner of medical problems-from respiratory prob-lems such as wheezing to more serious conditions like depression.

Mould and asthma

A condition that's been consistently linked to household mould is asthma-particularly in children. While several studies have shown that mould can exacerbate its symptoms, new evidence suggests that it can even cause asthma to develop if children are exposed to it early on in life.

Using the Asthma Predictive Index (API), researchers from the University of Cincinnati in Ohio, USA, evaluated the risk of future asthma among 483 children with and without visible mould growing in their homes. They discovered that three-year-old children living with high levels of visible mould in the home during early infancy were seven times more likely to have a positive API, suggesting an increased risk of asthma, than those living with no visible mould (Ann Allergy Asthma Immunol, 2009; 102: 131-7).

Other studies have also reported similar findings. In one involving nearly 2000 UK children, the presence of a mouldy smell in the home was a greater determinant than heredity in predicting the develop-ment of childhood asthma (Environ Health Perspect, 2005; 113: 357-61).

In yet another study in school-age children, those exposed to either mould or "dampness" during the first year of life were at least twice as likely to suffer from asthma and respiratory symptoms such as cough, wheezing or phlegm as those free of such exposure. As the researchers concluded, "The results strengthen the evidence for a causal association between 'dampness' and respiratory health, pointing to its possible independent role in causing asthma" (Environ Res, 2009; 109: 59-65).

Indoor mould has been linked to asthma in adults, too (Environ Health Perspect, 2002; 110: 543-7). Indeed, looking at the facts and figures for children and adults together, it can be estimated that 21 per cent of all current asthma cases in the US may well be attributable to dampness and mould in the home, as well as in schools, offices and institutional buildings. This means that, of the approximately 22 million people with asthma in the US, nearly five million cases may be due to damp and mould exposure indoors (Indoor Air, 2007; 17: 226-35).

Conventional medicine's answer to asthma is hazardous drugs such as steroids and long-acting beta-2 agonists. Yet, looking at the evidence, it appears that simply tackling mould and mildew (mould growing on fabric) in the home will ease or even cure the problem for millions of asthma sufferers.

Other health effects

Besides asthma and respiratory symptoms, indoor mould has also been associated with a range of other health problems, including headache, fever, excessive fatigue, cognitive and neuropsychological effects, gastro-intestinal symptoms and joint pain-although the evidence still requires further investigation (Can Fam Physician, 2002; 48: 298-302).

Perhaps one of the most intriguing connections is that between house-hold mould and depression. Using survey data from eight European cities compiled by the World Health Organization (WHO) in 2002 and 2003, researchers from Brown University in Providence, RI, found that people living in damp, mouldy households were 34- to 44-per-cent more likely to have a diagnosis of depression than the residents of mould-free homes (Am J Public Health, 2007; 97: 1893-9).

Interestingly, the increased risk of depression was also associated with the resident's perception that such a damp, mouldy environment cannot be controlled as well as with docu-mented physical health problems linked to mould exposure. As lead researcher Edmond Shenassa explained, "If you are sick from mould and feel you can't get rid of it, it may affect your mental health."

However, it cannot be ruled out that exposure to mould may also somehow alter the behavioural and biochemical brain pathways involved in depression. Shenassa and his team are currently conducting animal studies to investigate whether this is the case (Environ Health Perspect, 2007; 115: A536).

Yet another concern is that mould exposure could lead to cancer. At present, clear evidence is lacking, although one study found that women exposed to moulds at work-of agricultural and industrial origins-were two to three times more likely to have cervical and lip cancers (Occup Environ Med, 2008; 65: 489-93). Whether the moulds found in homes have a similar effect remains to be seen.

Mould and its toxic effects

Although it looks as if mould clings to the surfaces it grows on, in fact, as it multiplies, tiny spores are released into the air, where they are easily inhaled. According to Canadian researchers Norman King and Pierre Auger, mould can then affect the body in a number of ways (Can Fam Physician, 2002; 48: 298-302).

First, mould can trigger allergic reactions such as asthma or a runny nose. Heavy and repeated exposures can lead to hypersensitivity pneumo-nitis, an inflammation of the alveoli (air sacs) within the lungs.

Second, mould produces various volatile organic compounds (VOCs), such as alcohols and ketones, which are known irritants-and responsible for that characteristic musty odour. Headaches, dizziness, fatigue and other systemic effects may result from this type of exposure.

Third, certain species of mould produce mycotoxins, natural organic compounds that initiate a toxic response. These mycotoxins have been linked to immunosupression, skin irritation and even pulmonary haemorrhage in infants (see box, page 20).

Last of all, some types of mould can cause infectious diseases in those who have weakened immune systems (for example, bone-marrow-trans-plant patients). Such infections can affect the skin, eyes, lungs and other organs.

Living with mould

Although mould has been around for centuries, mould-related health problems appear to have arisen only recently. There are various explana-tions for this trend, and one of the most compelling is the substantial worldwide increase in the use of air conditioning.

According to the head scientist at the indoor environment department of the Lawrence Berkeley National Laboratory-part of the US Depart-ment of Energy-in Berkeley, CA, more than 15 studies point to a strong link between air conditioning and numerous respiratory symptoms. Microbes thriving in air-conditioning systems, including mould and bacteria, are probably contributing to the relationship (Environ Health Perspect, 2007; 115: A300-5).

Other factors that might also have an impact include poorly built homes and an increase in the numbers of individuals who have weak or stressed immune systems. Those who suffer from chronic illness, the elderly and even pregnant women are among the groups that have been identified as being potentially more vulnerable to exposures to mouldy indoor spaces.

Yet, despite the mountain of research, a number of gaps in the evidence remain to be filled, partic-ularly as regards systemic effects. Still, as Bob Weinhold writes in his 2007 report, A Spreading Concern: Inhalational Effects of Mold, many organizations around the world are reaching the same conclusion: "Don't mess with mould. If you can see it or smell it-and especially if health problems are occurring-clean it out, throw it out, or get out" (Environ Health Perspect, 2007; 115: A300-5).

Joanna Evans

Murderous mould?

In the 1990s, a series of reports associated exposure to damp and mould (especially of the species Stachybotrys chartarum, also known as S. atra) in homes in Cleveland, Ohio, with an outbreak of acute idiopathic pulmonary haemorrhage in infants (AIPHI). This condition, involving the rupture of capillaries in the lungs, refers to its sudden onset in a previously healthy infant (see www.cdc.gov/mold/AIPHIcasedef.htm for more information).

Following the deaths of a number of infants as a result of this condition, an investigation by the US Centers for Disease Control and Prevention (CDC) suggested that AIPHI was associated with major household water damage over the six months prior to the illness, along with increased levels of household mould, including the toxin-producing S. chartarum (Environ Health Perspect, 1999; 107 Suppl 3: 495-9; JAMA, 2000; 283: 1951-3).

Although researchers have since concluded that there is insufficient evidence to confirm that mould exposure is a cause of AIPHI-mainly due to study limitations such as problems with data collection and the methods used to assess exposure-additional reports from independent sources and studies in animals have provided further evidence of plausibility for such a causal connection (Pediatrics, 2006; 118: 2582-6).

Indeed, as the lungs in young infants are growing rapidly, they may be particularly sensitive to toxin-containing mould spores, which could lead to areas of capillary fragility. Coupled with other stresses to the developing lungs such as from tobacco smoke-also found to be present in most of the Cleveland infants' homes-mould exposure could eventually trigger lung haemorrhages (Environ Health Perspect, 1999; 107 Suppl 3: 495-9).

Mould prevention tips

Mould spores are ubiquitous in the environment and it's impossible to maintain a completely mould-free home. However, the following will help to prevent spores from colonizing and growing.

- Keep all materials and surfaces as clean and dry as possible

- For surfaces where moisture frequently collects, clean them with a baking-soda solution one day and with vinegar the next

- Fix plumbing leaks and other water problems as soon as possible

- Increase ventilation (run a fan or open a window) in damp-prone spaces such as bathrooms

- If condensation is a problem, consider installing a dehumidifier to reduce the humidity, but be sure to clean the device regularly

- Vent appliances that produce moisture, such as clothes dryers and stoves, to the outside wherever possible

- Open cupboards and drawers regularly to allow air to circulate

- Remove or replace carpets and upholstery that have been soaked and cannot be dried quickly

- Avoid using carpet in moisture-prone rooms or spaces such as bathrooms and basements

- Cover cold surfaces, such as cold-water pipes, with insulation

- If flooding occurs, clean up and dry out your home promptly and thoroughly (preferably within 24-48 hours).